As measures for improving the reliability of a PLC, there has been proposed doubling constituent unit of the PLC. By doubling the constituent unit, it is possible for the PLC to continue controlling by using the other constituent unit even if one constituent unit fails. As a representative example of a constituent unit to be doubled, there has been known a power supply unit (a power supply device) in which many life-limited components are incorporated.
To double the power supply unit, it is necessary to consider how to set the ratio of an output from each power supply unit. For example, Patent Literature 1 discloses a technique for equalizing the ratio of outputs from two power supply units.